DAIRY LABORATORY 
GUIDE 



H.E. ROSS 




Class r SFZf^ 

Book Eh 

GopgtitN?- 






COPYRIGHT DEPOSIT. 



A DAIRY 

LABORATORY 

GUIDE 






ROSS 

ll 
Assistant Professor of Dairy Industry 

New York State College of Agriculture at Cornell University 



NEW YORK 

ORANGE JUDD COMPANY 

1914 



SFZ53 



Copyright, 1910-1914, by 

ORANGE JUDD COMPANY 

All Rights Reserved 



APR 29 1914 



Printed in the U. S. A. 

©CI.A369907 



PREFACE 

In the study of any science the student should, 
so far as possible, work out his own problems. Yet 
the beginner may be saved much useless time and 
labor by helpful suggestions at the proper time. 
This Manual is designed as a guide to students in 
dairy laboratory work, with just enough explana- 
tion given to supplement the exercises which are 
outlined in the Manual. It is not intended for a 
text book and should not be used in the place of 
one. 

The author's thanks are due Prof. W. A. Stock- 
ing, Jr., for many helpful suggestions in the ar- 
rangement and preparation of this book. 

The author recognizes that a book of this kind 
needs frequent revision, and an eflfort will be made 
to keep this Manual up to date. 

H. E. Ross. 
Dairy Laboratories^ 
New York State College of Agriculture^ 
at Cornell University, 

August 31, 1910 



m 



TABLE OF CONTENTS 

I 

The Composition of Alilk i 

II 
Explanation. The Babcock Test 5 

III 

Explanation of Boiled 2^1 ilk Test and Formalde- 
hyde Test 18 

IV 

Explanation. Mixing Samples of Butter Be- 
fore Testing for Fat and Moisture 19 

V 

Explanation. The C. U. Butter IMoisture Test 23 

VI 

Explanation. The Specific Gravity of i\Iilk and 
the Lactometer 



-/ 



VII 
Explanation. The Board of Health Lactometer 37 



vi DAIRY LABORATORY GUIDE 

VIII 

Explanation. Use of the Hand Machine in 

Babcock Test 38 

IX 
Explanation. The Acidity of Milk 43 

X 

Explanation. The Effect of Speed of Machine 

on the Babcock Test 51 

XI 
Explanation. Commercial Rennet and Its Use. 69 



A Dairy Laboratory Guide 



THE COMPOSITION OF MILK 

Milk is composed of a great many f"bstances 
but ■ so far as the dairyman is concerned, there are 
only six constituents which are of pnme impor- 
tance The following table gives the constituents 
of milk, together with the per cent of each, ob- 
tained by a large number of analyses: 

Water 87.opercent 

Fat 4.0 per cent 

Casein 2.6 per cent 

Sugar S.opercent 

Albumen 0.7 per cent 

Ash o.7percent 

Although in the above table the different con- 
stituents are given definite per cents, yet the com- 
nosition of normal milk is very variable. Ihe 
Sineeds no discussion, as it is just like the water 
found anywhere else m nature. , . ^ , 

Fat is present in milk in the form of minute drop- 
lets or globules. These globules are distributed 
throughout the milk and are not in solution but 
in fine suspension. This state is called an muteo». 
It was disputed for a long time as to whether or not 
the fat globule had a membrane around it. It is 
now believed by the best authorities that the at 
<rIobule has no membrane, but that the droplet 



2. A DAIRY LABORATORY GUIDE 

keeps its circular form because of its power of con- 
densing upon its surface the serum of the milk. 
The size of the fat globules differ in milk from 
different breeds of cows, and it is supposed that the 
larger the fat globules the more easily they rise to 
the surface when the milk is left standing in a 
vessel. 

Butter is composed largely of fat, so we speak of 
the fat of milk as butter fat. 

Fat is the most important constituent of the 
milk, because milk which contains a fair amount of 
butter fat is more valuable as a food than a milk 
Avhich is poor in fat. The other food constituents 
of the milk usually increase or decrease as the fat 
increases or decreases. This is true, however, only 
within certain limits. 

Fat is an important constituent of nearly all of 
the products of milk, so that in most cases a milk 
rich in fat is more valuable for manufacturing pur- 
poses than a milk poor in fat. 

On account of the importance of the fat, it is 
made oftentimes a basis of payment for milk. 

Butter fat is composed mainly of nine different 
fats. There are a few fats which are present in 
such minute quantities that they are of no prac- 
tical importance. All of the fats have the same 
basis, namel}'', glycerin, and the fat is made by the 
chemical union of glycerin "and the corresponding 
fatty acid. For example, the fat butyrin is made 
of glycerin and butyric acid. The fat stearin is 
made of stearic acid and glycerin. While the com- 
position of the different butter fats are knowm. yet 
the chemist is unable to make them in the labora- 
tory. 

The fats of butter fat are divided into two main 
groups, the volatile and nonvolatile, and are so 



A DAIRY LABORATORY GUIDE 3 

named because they are made respectively from 
volatile and nonvolatile fatty acids. 

The fats under each class are as follows : 

VOLATILE NONVOLATILE 

Butyrin Olein 

Caprin Myristin 

Caproin Palmatin 

Caprillin Stearin 
Laurin 

There is some dispute as to whether laurin is a 
volatile or nonvolatile fat, but it is usually consid- 
ered volatile. The volatile fats compose about 8 
per cent and the nonvolatile about 92 per cent of 
butter fat. The fats of butter fat have dififerent 
characteristics and properties, and one chief dif- 
ference of fats is their melting point. For example 
the melting point of stearin is about 143° F., and 
the melting point of olein is about 40° F. A varia- 
tion in the amount of either of these two fats would 
necessarily cause the melting point of butter fat to 
vary. The melting point of butter fat is usually 
between 92° F. and 96° F. 

Casein is the chief proteid compound of milk, and 
forms about 20 per cent to 23 per cent of the milk 
solids. It exists in milk in very fine suspension, 
and is held in suspension by the salts of calcium. 
It is, therefore, sometimes called calcium casein. 
The casein is in such a fine state of suspension that 
it cannot be filtered out of the milk by any ordinary 
means. This fine state of suspension is called the 
colloidal state. When milk sours naturall}^ and 
enough acid is found to unite with the lime salts 
of the milk, the casein is precipitated. Casein is 
also precipitated by any acid and rennet or pepsin. 
Casein is A^aluable as food both in raw milk and in 



4 A DAIRY LABORATORY GUIDE 

the products of milk, such as the various kinds of 
cheese. It is also used commercially in many 
ways, some of them being as a substitute for cel- 
luloid in the manufacture of buttons and toilet 
articles. It is also used in cold water paints. By 
a new process it is said that casein is now being 
made into a substitute for ivory, making excellent 
table tops, mantels, etc. 

Sugar forms about 37 per cent to 39 per cent of 
the milk solids. The chief value of milk sugar is- 
its food value in milk. It is also used in pharmacy 
in mixing powders, coating pills, etc. Milk sugar 
is not used very extensively commercially because 
of the expensive cost of manufacture. It is not 
as sweet as cane sugar, because it is not as soluble. 
It has the same chemical formula (C12H22O11) 
as cane sugar. Acid is produced naturally in milk- 
by the action of bacteria upon the milk sugar. 

The albumen in milk is in solution. It is valu- 
able chiefly as a food in milk. It has one commer- 
cial use in the manufacture of Italian cheese. This 
cheese is made where large quantities of whey are 
produced. The whey is heated nearly to the boil- 
ing point, and this heat precipitates the albumen. 
The/whey is then drawn off and the albumen is 
dipped into molds. The cheese made from albumen 
forms a very good, nutritious food. 

The ash is the part of milk left after burning, and 
it is the most constant constituent of the milk. 
It very rarely goes below .68 per cent or above .J2 
per cent. It consists chiefly of the phosphates of 
calcium and the chlorides of sodium, potassium, 
iron and magnesia. 

Ash is important as a food in furnishing the- 
mineral constituents for the body. 



A DAIRY LABORATORY GUIDE 5 

THE BABCOCK TEST 

The Babcock test is a test for the per cent of fat 
in milk and its products. It was invented by Dr. 
S. M. Babcock, chief chemist for the experiment sta- 
tion at Wisconsin, and a description of the test was 
published in a report of 1890 from that station. 
The instrument used to measure the milk is called 
a pipette and holds up to its graduated mark 17.6 
cc. Since milk is somewhat viscous, the pipette 
will deliver on an average 17.44 cc, which is for 
all practical purposes 18 grams. In using the 
pipette the milk is drawn above the 17.6 cc. mark 
and the soft part of the index finger placed quickly 
over the pipette. The column of milk can be 
easily controlled and allowed to flow out until it is 
on a level with the 17.6 cc. mark. The pipette 
should always be held so that the 17.6 cc. mark is 
on a level with the eye. The sample to be tested 
is measured into a special bottle with a graduated 
neck, holding a column of melted fat which is a 
definite per cent by weight of the 18 grams of milk 
taken. In adding the milk to the bottle the latter 
should be held in a slanting position, so that the 
milk will run down the lower inside of the bottle 
neck and will not be forced out by the outcoming 
air. 

After measuring the milk into the bottle, 17.5 
cc. of sulphuric acid (H2SO4) of a specific gravity 
of 1.82 to 1.83 is added and the milk and acid at 
once thoroughly mixed. The acid burns up (by 
moist combustion) everything in the milk except- 
ing the fat. The same precautions should be ob- 
served in adding the acid as in adding the milk, 
namely, to slant the bottle, and the bottle should be 
revolved as the acid is poured in, so that all of 



6 A DAIRY LABORATORY CUIDE 

the milk adhering to the neck of the bottle 
will be washed down. The vessel contain- 
ing the acid should be kept corked in order 
to prevent the acid taking up moisture from the air 
and becoming too weak for use. If the acid is too 
weak more than 17.5 cc. are used, and if too strong 
less than 17.5 cc. are used. Good acid is colorless, 
although it may be quite dark and at the same time 
be useful for the Babcock test. It must, in any 
case, be free from undissolved foreign particles. 

After adding the acid to the milk the bottles are 
placed in a centrifugal machine and whirled. Care 
should be taken to have the machine balanced, i. c, 
for every bottle on one side of the machine there 
should be a corresponding bottle on the opposite 
side of the machine. The bottles are centrifugalized 
for five minutes and then filled with hot water up 
to the base of the neck. Centrifugalizing is then 
continued for two minutes more and hot water is 
added to bring the fat into the graduated neck. The 
centrifuge is then run for one minute. 

The bottles are then ready to read, and in case 
of whole milk one should read between the extreme 
points of the fat column. This method of reading, 
by comparison with the chemical method, has been 
found to make up for the fat which remains in 
the bottom of the bottle and cannot be removed by 
centrifugalizing. The bottles should be read at a tem- 
perature of 120° F. It is no trouble to obtain this 
temperature if centrifuging has been done with a 
steam machine. Where the machine is filled with 
steam the bottles should stand for from thirty 
seconds to one minute in a room at ordinary tem- 
perature to allow excess of heat to pass ofif before 
reading. If a hand machine is used the tester must 
have hot water placed in it to obtain the required 



A DAIRY LABORATORY GUIDE 7 

temperature. This is especially necessary if the 
testing is being done in a cold room. 

The machine should always be kept well oiled 
and securely fastened to the support on which it is 
being operated. Skimmed milk contains such a 
small amount of fat that the fat column could not be 
read in an ordinary whole milk bottle. A bottle is, 
therefore, used which has a neck with a small bore. 
This neck is so small that the milk and acid could 
not 'be poured through it, so a funnel tube is pro- 
vided for this purpose. The skimmed milk bottle 
should be placed in the machine in such a position 
that the funnel tube will be on the outside. This 
w^ill prevent fat lodging in the space between the 
tube and the wall of the bottle. 

The sulphuric acid is added to the milk to 
destroy all of the milk solids except the fat, and the 
chief solid to be destroyed is the casein. Skimmed 
milk contains proportionately more casein than 
does whole milk and, therefore, in making a Bab- 
cock test of skimmed milk 2 cc. extra of sulphuric 
acid should be used. The fat globules in skimmed 
milk are small in size and correspondingly hard to 
remove. A Babcock sample of skimmed milk 
should, therefore, be whirled ten minutes, two 
minutes and one minute. 

Cream is so viscous that it cannot be measured 
accurately into a test bottle by means of a pipette. 
It should always be weighed. The New York state 
dairy laws now consider it a misdemeanor to meas- 
ure cream for testing where the tests are used as a 
basis of payment for butter fat. 

Because the cream is sometimes too rich in butter 
fat to be tested in an ordinary cream bottle, 9 
grams are tested in an 18-gram bottle and the result 
multiplied by two. Nine-gram cream bottles are 



8 A DAIRY LABORATORY GUIDE 

also coming into common use. These bottles give 
the reading direct without any computation. In 
testing 9 grams one would naturally use one-half 
the usual amount of sulphuric acid. On account, 
however, of the large proportion of fat present, the 
acid is liable to char the fat ; and for this reason it 
is better to add approximately 9 grams of water 
and then add a little less than the usual amount of 
acid. 

The fat column in the neck of a cream bottle is so 
large that its volume is affected by temperature. It 
is necessary to read the bottles at some constant tem- 
perature and the most accurate readings are ob- 
tained at temperatures from 130° F. to 140° F. In 
order to obtain the proper temperature the bottle 
should be allowed to stand for at least three minutes 
in a water bath, care being taken to have the water 
in the bath as high as the fat column in the bottle 
neck. 

The meniscus on the fat column of a cream bottle 
is large and is not constant so that no rule for in- 
cluding it in the reading can be formulated. The 
practice is, therefore, followed of removing the 
meniscus by adding a few drops of glymol (white 
mineral oil) to the top of the fat column after the 
test is completed. This flattens the top of the fat 
column and gives the best results of any method 
yet devised. The glymol is easier to use if colored 
pink with alkana root. 

Butter is tested in the cream bottles, from 3 to 4 
grams being used for the test. Enough warm 
water is added to bring the sample up to approx- 
imately 18 grams, and from 10 to 12 cc. of the sul- 
phuric acid are used. 

Cheese is also tested in the cream bottle, 4 to 5 
grams being used. The cheese must first be minced 



A DAIRY LABORATORY GUIDE 9 

with a knife as fine as possible in order to make it 
possible for the acid to dissolve all of the casein. 
After the cheese is weighed into the bottle, about 
5 cc. of hot water are added and the mixture shaken 
vigorously for two or three minutes. This softens 
the casein. Enough warm water is then added to 
bring the sample to approximately i8 grams. The 
sample is again shaken for two or three minutes, 
and the ordinary amount of H2SO4 is then added. 
If the cheese is old and dry, 2 or 3 cc. of H2SO4 in 
excess of the usual amount are sometimes necessary 
to dissolve the casein. In mincing the cheese the 
sample should not be allowed to dry out any more 
than is absolutely necessary. 

In the cases of both the butter and the cheese, 
the results obtained must be reduced to an 18-gram 
basis, when an 18-gram bottle is used. This can be 
done by dividing the per cent obtained by the num- 
ber of grams used and multiply the quotient by 18. 

Whey is usually tested in whole milk bottles, 
although it is best to test it in skimmed milk bot- 
tles when possible. The right bottle to use can 
only be determined by actual experiment. Whey 
requires less acid than whole milk, usually about 
12 cc. 



EXERCISES 



12 A DAIRY LABORATORY GUIDE 

EXERCISE I 
THE BABCOCK TEST 

1. Draw the milk above the mark on the pipette 

and allow the milk to settle just to the mark. 
Repeat this until some proficiency in the use of 

the pipette is obtained. 
What two special precautions are to be observed 

in handling the pipette? 

2. Test by the Babcock method a sample of whole 

milk. Perform this test before doing either 
3 or 4. 

3. Measure out into your white cup 50 cc. of the 

same sample of milk used in experiment 2. 
Add to this 15 cc. of water. Mix thoroughly 
and test in duplicate by the Babcock method. 

4. Using milk from the same sample as used in 

experiment 2, measure out 50 cc. of milk and 
add to it 15 cc. of skimmed milk. Mix thor- 
oughly and test in duplicate by the Babcock 
method. 
Did you obtain the most fat in experiment 3 or 
experiment 4? Include in your notes a brief 
description of the Babcock test. 



A DAIRY LABORATORY GUIDE 13 

STUDENT'S NOTES AND REPORT 



14 A DAIRY LABORATORY GUIDE 

STUDENT'S NOTES AND REPORT 



A DAIRY LABORATORY GUIDE 1 5 

EXERCISE II 

BABCOCK TEST 

Test by the Babcock method a sample of whole 
milk, skimmed milk and cream. 

Weigh into some convenient dish i8 grams of 
cream just tested. Add to it 20 grams of the 
whole milk just tested. Compute the per 
cent of fat in the mixture and verify your 
computation by testing the mixture by the 
Babcock method. 

Test by the Babcock method a sample of butter- 
milk. 

STUDENTS NOTES AND REPORT 



1 6 A DAIRY LABORATORY GUIDE 

EXERCISE III 
BABCOCK TEST 

1. Test in duplicate a sample of whole milk, 

skimmed milk and cream. Test the skimmed 
milk in the same way that the whole milk is 
tested. 

Why is cream taken by weight instead of by 
volume? 

Why are 9 grams used instead of 18 grams? 

When 9 grams of cream are tested in an 18- 
gram bottle, what correction has to be made 
in the result and why? 

2. Retest the cream and skimmed milk. Add acid 

to the skimmed milk about one-fourth of an 
inch above the mark on the acid measure and 
whirl ten minutes the first time, two minutes 
the second time and one minute the third 
time. 

In retesting the cream do not add water, and 
use one-half the usual amount of acid. 

In order to save time the cream and skimmed 
milk may be whirled together. 

Explain fully the object of using extra acid and 
whirling an extra length of time in testing 
skimmed milk. 

Record carefully any difference in the appear- 
ance of the fat column of the cream in ex- 
periments I and 2. 

What should be the appearance of an ideal fat 
column in a completed Babcock test? 



A DAIRY LABORATORY GUIDE I? 

STUDENT'S NOTES AND REPORT 



l8 A DAIRY LABORATORY GUIDE 

EXPLANATION OF BOILED MILK TEST 
AND FORMALDEHYDE TEST 

There are two principal tests for boiled milk. 
One test makes use of three chemicals — hydrogen 
peroxide, potassium iodide and starch. In the 
second test two reagents are employed — hydrogen 
peroxide and paraphenylenediaminehydrochloride. 
In both cases a blue color results if the milk has 
not been boiled. If the milk has been boiled no 
blue color will result. The last named test acts 
more rapidly than the first one and also gives a 
more intense color. Any double oxide may be sub- 
stituted in place of the hydrogen peroxide. Such a 
double oxide would be calcium peroxide. There is 
in milk an enzyme galactase which is destro^^ed by 
heat. When the milk has not been heated this 
enzyme sets free the oxygen from the oxidizing 
agent, and in case of the first test, the free oxygen 
splits up the potassium iodide and liberates free 
iodine. The starch in the presence of free iodine 
turns blue. In case of the second test the oxygen 
liberated by the galactase acts directly on the 
paraphen3denediaminehydrochloride and turns the 
solution blue. Hydrogen peroxide often contains 
sulphuric acid. AMien this is the case, the reagent 
is useless for the test with starch, as the free acid 
would break up the potassium iodide. If this hap- 
pened a blue color would result whether the milk 
had been heated or not. 

The test for formaldehyde is a delicate one and 
is easy to perform, inasmuch as it may be done in 
connection with the Babcock test. The regular 
amount of milk is measured with the 17.6 cc. pipette 
into a Babcock test bottle and a few drops of ferric 
chloride added. The regular amount of sulphuric 



A DAIRY LABORATORY GUIDE 1 9 

acid is next added, and if formaldehyde is present 
a lavender-colored ring will appear between the 
javer of acid and the layer of milk. If the contents 
of the bottle are slowly mixed the dissolving casein 
will take on a lavender color. The test w^ill not 
w^ork if the milk is too old or if too much of the 
formaldehyde has been added to the milk. 

Sometimes sulphuric acid contains ferric salts as 
an impurity; and when such is the case, the acid 
w^ill give the test for formaldehyde without the use 
of ferric chloride. It is best however, to always 
add the ferric chloride to make sure there is a ferric 
salt present. 

EXPLANATION. MIXING SAMPLES OF 

BUTTER BEFORE TESTING FOR FAT 

OR MOISTURE 

Before testing a sample of butter for either 
moisture or fat the sample should be thoroughly 
mixed. Fat and water do not readily mix, and 
special precautions must be taken to make the 
sample uniform throughout. The butter should be 
heated and stirred until it is about the consistency 
of thick cream. Do not heat the butter too much, 
?^ tne w^ater and fat will entirelv separate and it is 
difficult to remix them. The sample should 
then be cooled and stirred thoroughly while 
cooling, else the fat will cool rapidly on the 
outside and force all of the water towards 
the middle of the sample. The cooling process 
should be kept up until the sample is quite firm. 
The heating and cooling may be accomplished by 
placing the butter in any convenient vessel, such 
as a glass-stoppered sample jar. The jar may then 
be held under a water faucet or set in a dish of 
water. 



20 A DAIRY LABORATORY GUIDE 

EXERCISE IV 
BABCOCK TEST 

1. Test by the Babcock method a sample of whole 

milk, skimmed milk and butter. 
]\Iix the butter properly before weighing it out 
for the test. 

2. Measure out about 36 grams of skimmed milk 

(Babcock pipette twice full to the mark). 
Divide approximately into four parts. Test 
two of these parts for boiling by two dif- 
ferent methods. Boil the remaining 18 
grams, divide approximately into two parts 
and test for boiling by two different methods. 
Give the chemicals used in each case. Do 
not add the chemicals to the milk while the 
milk is hot. 

3. Measure out in duplicate a sample of skimmea 

milk as for the Babcock test. Before adding 
the sulphuric acid dip your stirring rod into 
the formaldehyde and rinse it off in one of 
the samples. Then add to both samples the 
ferric chloride and sulphuric acid and note 
the difference in color due to formaldehyde. 

4. Test for formaldehyde any four of the samples 

furnished. Report the results by number. 
Sometimes sulphuric acid will alone give the 

color test for formaldehyde. Why is this? 
Why is it best to always add the ferric chloride 

when making the formaldehyde test? 



A DAIRY LABORATORY GUIDE 21 

STUDENT'S NOTES AND REPORT 



^^ A DAIRY LABORATORY GUIDE 

STUDENT'S NOTES AND REPORT 



A DAIRY LABORATORY GUIDE 23 

THE CORNELL BUTTER MOISTURE TEST 

When butter is heated over a flame, the casein 
forms a snow-white blanket over the surface of the 
butter. By a comparison with the chemical method 
it has been found that when the butter loses its 
snow-white color and turns a dirty brown color the 
sample has given up its moisture. When this 
brown color has appeared it is time to remove the 
sample from the flame. Heating butter in a direct 
flame is liable to volatilize some of the butter, even 
before all of the water has been given off. In order 
to do away with this danger a sheet of asbestos is 
placed between the flame and the container ot the 
sample. The asbestos so tempers the flame that 
while a high heat is produced, the danger of sud- 
denly volatilizing the butter is largely done away 
with. 

The scales used are made especially for use in 
butter-moisture work. They are so constructed 
that after the moisture is driven off, each notch 
the large weight is reversed equals i per cent of 
moisture driven off, and each notch that the small 
weight is reversed equals .i per cent of moisture 
driven off. Alwavs allow the sample to cool be- 
fore weighing. While the sample is cooling it Is 
well to cover it with something Ta sheet of paper 
will do), ^o that the sample will not take water 
from the air. 



24 A DAIRY LABORATORY GUIDE 



EXERCISE V 

BABCOCK TEST AND BUTTER MOISTURE 
TEST 

I. Prepare a sample of butter for the moisture test 
and test by the Cornell method. 

2. Test a sample of milk in the ordinary way. 
Retest the same sample in duplicate, using only 

9 grams of the sample. (It must be weighed 
out.) Make the sample up to i8 grams by 
adding water. Add the usual amount of 
acid. 

3. Test a sample of cream in the ordinary way. 
Retest the cream in the whole milk bottle, divid- 
ing 18 grams between four bottles (4^^ 
grams by weight in each bottle). 

In each case add enough water to bring the 
sample up to 18 grams and then add the 
proper amount of acid as indicated by the 
appearance of the sample. Add the acid 
slowly, a little at a time, and shake thor- 
oughly. 



A DAIRY LABORATORY GUIDE 25 

STUDENT'S NOTES AND REPORT 



26 A DAIRY LABORATORY GUIDE 

STUDENT'S NOTES AND REPORT 



A DAIRY LABORATORY GUIDE IJ 

THE SPECIFIC GRAVITY OF MILK AND 
THE LACTOMETER 

The specific gravity or density of a substance is 
a ratio between the weight of a given volume of 
the substance and the weight of a given volume of 
some other substance taken as a standard. The 
standard for liquids is water and its specific gravity 
is taken as one. Milk is slightly heavier than water, 
and the specific gravity of normal milk av^erages 
1.032, and the specific varies from 1.029 to 1.035- 
If we add water to milk the specific gravity is 
lowered, because water is lighter than milk ; and if 
we skim milk we take away fat which is lighter 
than milk and the specific gravity is increased. 
When the water is added to milk the effect is the 
same as it would be if the solids were actually re- 
moved from the milk. This is true because the 
solids which were distributed throughout a given 
volume on the addition of water, have to 
distribute themselves throughout the increased 
volume of the liquid. For this reason we say 
that the addition of water to milk " decreases " 
the total solids, and it is a fact that when water is 
added to milk all of the solids are decreased in the 
same proportion. It is important to remember 
this fact when one is figuring out the per cent of 
adulteration of milk. 

The Lactometer. — The instrument used to 
measure the specific gravity of a liquid is called a 
hydrometer, and there are many kinds of specialized 
hydrometers. The hydrometer used to test the 
density of milk is called a lactometer, and, for the 
most part, only two kinds are used. One is the 
Quevenne (called Q. for abbreviation) and the other 
is called the Ordinary, or Nezv York State Board of 



28 A DAIRY LABORATORY GUIDE 

Health (commonly called the B. of H. lactometer). 

The Quevenne lactometer has a long, narrow 
stem which is extended into a hollow glass tube of 
much larger diameter than the stem itself. At the 
lower end of the instrument is a bulb of mercury 
which causes the lactometer to sink in the liquid 
to its proper level. The upper part of the stem 
contains a thermometer scale, as it is important to 
know the temperature of the milk when the lac- 
tometer reading is taken. This scale does not re- 
cord high temperature, and, therefore, the instru- 
ment should never be placed in hot liquids. In 
order to clean the lactometer wash in cool water 
and wipe with a dry cloth. Immediately below the 
thermometer scale is a lactometer scale with num- 
bers ranging from 15 to 45, the lowest readings 
being at the upper end of the scale. One may ob- 
tain the specific gravity reading by prefixing i.o 
before the lactometer reading. Thus, if the in- 
strument gives a reading of 33, the specific gravity 
would be 1.033. The fact that the Quevenne lac- 
tometer gives specific gravity readings directly is 
one of its chief advantages. 

Temperature afifects the density of liquids. The 
colder the milk the more dense it is, and the warmer 
the milk the less dense it is. For this reason lac- 
tometers are standardized to give readings at a 
temperature of 60° F. When milk is warmer or 
colder than 60° F. a correction must be made, and 
this correction for the Quevenne is .1 of a lactometer 
degree for every degree in temperature that the 
sample is above or below the standard temperature. 
When we cool the milk down we add ; when we 
warm the milk we subtract. For example, if a 
lactometer gave a reading of 32 at a temperature 
of 66° F., we would add .6 (.1X6) to the lactometer 



A DAIRY LABORATORY GUIDE 29 

reading, making the corrected or true reading 32.6. 
In this case the specific gravity would be 1.0326. 

Familiarity with the action of the lactometer may 
be obtained by working theoretical problems, of 
which the following is an illustration: If the 
lactometer reading of a sample of milk is 31.5 at 
62° F., what would be the reading at 57° F.? In 
this case 57° F. becomes our standard, because it is 
the temperature to which we are going to lower the 
sample. Since the sample is 5 degrees too warm, 
•5 (-iXS) of a lactometer degree must be added to 
the lactometer reading, making the true or cor- 
rected lactometer reading 32. 

When used in connection with theBabcock test the 
lactometer reading is important in obtaining the total 
solids and solids not fat of milk. There are several 
of these formulae in use, and while they do not give 
quite as accurate results as the chemical method, 
they give results which are accurate enough for all 
practical purposes. They are as follows : 

1. '-i^=S. N. F. Babcock's formulae. 

2. ^=S. N. F. Troy's formulae. 

3. ^ L+.2f+.i4=S. N. F. Babcock's modi- 

fied formula. 

Generally speaking, the first formula gives the 
highest results, the second next highest and the 
third the lowest results. One can find the total 
solids by adding the fat reading to the solids not 
fat. In these formulae L stands for the lactometer 
reading and F for the fat reading. 

In using these formulae, the following precautions 
must be especially noted : Board of health readings 
can never be used in these formulae, consequently 
B. of H. readings must be changed to Q. ; specific 
gravity readings cannot be used ; the per cent of 
fat expressed in hundredths cannot be used. 



30 A DAIRY LABORATORY GUIDE 

An illustrative example will show how these 
formulae operate. Suppose the Q. lactometer read- 
ing of a sample of milk was 32.5 at 60° F. and the 
fat reading was 4.2 per cent, what are the solids 
not fat ? 

Formula= 

I. W-'=S. N. F. .7X4.2=2.94 
2.94+32.5=35.44 

3544-^3-8=9-32+ 
Formulating the above calculation: 

2^^5^^1=9.32% S. N. F. _ 

9.32+4.2'=i3.52 total solids. 
Using formula 2 : 

^=S. N. F. 

32.5+4.2=36.7 

36.7--4=9.i7+% S. N. F. 
Formulating the above calculation: 

2M±^=9.i7 S. N. F. 

9.17+4.2=13.37 T. S. 
Using formula 3 : 

i4L+.2f+.i4=S. N. F. 

32.5-^4=8.12 

.2X4-2=.84 

8.12+.84+. 14=9.10 S. N. F. 

9.10+4.2=13.30 T. S. 
By modifying Babcock's third formula the total 
solids may be obtained directly. It is as follows: 

M L+i.2f+.i4=T. S. 
Using the above lactometer and fat readings as 
an illustration, the formula would give the following 
results : 

32.5-^4=8.12 

i.2X4-2=504 

8.12+5.04+. 14=13.30% T. S. 



A DAIRY LABORATORY GUIDE 3 1 

The following- example will illustrate how a 
knowledge of the per cent of S. N. F. of a sample 
of milk is utilized in figuring adulteration per cents: 

Before adulteration a sample of milk had 4.2 per 
cent of fat and 9.0 per cent of S. N. F. After adul- 
teration the sample contained 3.1 per cent fat and 
7.5 per cent of S. N. F. The following questions 
can be answered from calculations with the above 
data: 

1. What per cent of water w^as added to the 

milk? 

2. At what rate per cent was the water added ? 

3. What per cent of the fat was adulterated 

by skimming? 

4. What per cent of the fat was adulterated 

by watering? 
(i) Since there were 9 parts of S. N. F. before 
adulteration and 7.5 parts of S. N. F. after adultera- 
tion, 1.5 must have been removed by adulteration. 

9— 7-5=1 -5 

1.5-^9=16.66% of S. N. F. removed by adding 
the water. 

Since 16.66 per cent of S. N. F. was removed, 
water is the only thing that could have taken its 
place; therefore 16.66 per cent of water was added 
to the milk. 

(2) For every 7.5 parts of S. X. F. in the milk 
1.5 parts were removed, or in other words water 
was added at the rate of 1.5 parts of water to every 
7.5 of S. N. F. 

The rate per cent at which water was added 
would be i.5-f-7.5=2o%. 

Before adulteration the sample had 4.2 parts fat 
and after adulteration 3.1 parts fat, i.i parts of fat 
were removed, which equals 26.19 P^^ cent. 
1. 1-^4. 2=^26.19%. 



7^2 A DAIRY LABORATORY GUIDE 

When milk is watered all of the solids are re- 
duced in the same proportion. It has been found that 
16.66 per cent of the S. N, F. was removed by water- 
ing; therefore, according to the above rule 16.66 per 
cent of the fat must have been removed by water- 
ing. But 26.19 per cent of the fat was removed; 
therefore the difference between 26.19 per cent and 
16.66 per cent will show what is removed by skim- 
ming; 26.19 — 16.66=9.53% removed by skimming. 



A DAIRY LABORATORY GUIDE 33 



EXERCISE VI 

BABCOCK TEST AND QUEVENNE 
LACTOMETER 

1. Test in duplicate by the Babcock method a 

sample of whole milk as follows : 

(a) Use ordinary amount of acid. 

(b) One-half usual amount of acid. 

(c) Fill the bottle up to the base of the 

neck with acid. 

(d) Use the regular amount of acid, but 

warm the acid and milk before mix- 
ing until they feel warm to the hand. 
Add the acid slowly to the sample. 
Observe and record all results care- 
fully. 
Test for fat a sample of butter. Why is it ad- 
visable to add the acid slowly in (d) ques- 
tion I? 

2. (a) Take a Ouevenne lactometer reading of a 

sample of whole milk and skimmed 
milk, making corrections for tempera- 
ture. 
Explain fully the effect of temperature on 
the lactometer readings. 
(b) Starting with the first reading in 2 (a), 
what would have been the reading if 
the temperature had been 54° F., 62° 
F., ys° F., 81° F.? 

3. Add one-half an acid measure of water to the 

skimmed milk sample and take the Ouevenne 



34 A DAIRY LABORATORY GUIDE 

reading-. Note any change in the lactometer 
reading, and explain the reasons for this 
change. 
4. Take the Qiievenne reading of a sample of 
skimmed milk. 

Compute what the reading would be if the tem- 
perature were four degrees higher. Verify 
your results by warming the sample and tak- 
ing the reading. Be sure to mix the sample 
thoroughly after warming it. Have the tem- 
perature of the milk low enough so that rais- 
ing the ternperature four degrees will not 
bring the sample above 70° F. Why should 
not the temperature be above 70° F.? 

What is the chief advantage of the Quevenne 
lactometer over other kinds? 



A DAIRY LABORATORY GUIDE 35 

STUDENT'S NOTES AND REPORT 



3^ A DAIRY LABORATORY GUIDE 

STUDENT'S NOTES AND REPORT 



A DAIRY LABORATORY GUIDE 37 

EXPLANATION. BOARD OF HEALTH 
LACTOMETER 

The Board of Health lactometer (commonly called 
E. of H. lactometer) is an instrument giving ar- 
bitrary readings and it must be changed to equiv- 
alent "^Ouevenne readings in order to obtain the 
specific'^ gravity. It is of the same general shape 
as the Quevenne, except that the thermometer 
scale is usually on the opposite side of the stem 
from the lactometer scale. The instrument is 
graduated from o to 120, and one degree Board of 
Health equals .29 of one degree Quevenne. In 
order, therefore, to change from Board of 
Health to Quevenne, the Board of Health 
reading is multiplied by .29. Vice versa to 
change from Quevenne to Board of Health reading, 
the Ouevenne reading is divided by .29. Like the 
Oue\'^enne, the Board of Health lactometer is gradu- 
ated to be read at a temperature of 60° F., and if 
the temperature is above or below the standard, 
the correction factor is .3 of one lactometer degree 
for every degree that the sample is above or below 
the standard. The following example will illustrate 
how correction is made: B. of H. reading 110.5 at 
65° F., what would be the reading at 60° F.? The 
sample must be cooled down 5 degrees ; therefore, 
Ave would add 1.5 (5X.3) to the reading (110.5), 
making a corrected reading of 1 12.0. One of the 
chief advantages of the B. of H. lactometer is that 
a small adulteration of the milk will make a notice- 
able change in the lactometer reading. This is be- 
cause the instrument has so large a scale. Also, 
when milk is watered, the number of lactometer 
degrees recorded below 100 indicates roughly the 
per cent of adulteration. 



38 A DAIRY LABORATORY GUIDE 

EXPLANATION. USE OF HAND MACHINE 
IN BABCOCK TEST 

It is a popular notion that milk cannot be tested 
accurately in a hand machine. This is a mistaken 
idea, as a hand machine should do as good work as 
any other machine. One of the chief reasons for 
inaccuracy in using a hand machine is the inatten- 
tion paid to the temperature. It is necessary to 
have the proper degree of heat in order to properly 
perform the Babcock test. To provide the proper 
temperature the hand machine should be filled with 
hot water up to the bottle cups if the room is at all 
cold. The small two-bottle and four-bottle hand 
testers have no frame, and so the bottle cups are 
made large in order that they may be filled with 
hot water if necessary. While it is not absolutely 
necessary to use hot water at all times, its use is 
always advisable. By its use the danger of test- 
ing milk at too cold a temperature is largely done 
away with. The operator should be careful to keep 
the machine to its proper speed during the entire 
run. 



A DAIRY LABORATORY GUIDE 39 



EXERCISE VII 

BABCOCK TEST AND B. OF H. 
LACTOMETER 

I Take the B. of H. lactometer reading and 
make a Babcock test of a sample of whole milk. Re- 
move the lactometer, and allow the milk to stand m 
vour lactometer cylinder while you do No. 2. i hen 
draw off from the top of the sample all the cream 
the pipette will hold. Then add to the sample 17.6 
cc of water and mix thoroughly. Again take a lacto- 
meter reading and make a Babcock test and hgure 
out the per cent of fat removed by skimmmg and 
the per cent of fat removed by watermg; make 
the test in the whole milk bottles. After drawmg 
off cream and adding water be sure to mix the sam- 
ple thoroughly. Upon what rule does your ability 
to do the above computation depend? Better results 
will be obtained if the milk is warmed to about «5 
F and allowed to stand as long as possible. In re- 
moving the cream keep the point ot the pipette as 
near as possible to the surface of the liquid. ^ 

2 Test in the steam machine whole milk, skim- 
med milk and butter. Run the skimmed milk ten 
minutes, two minutes and one minute, and use acid 
one-quarter inch above the mark on the acid meas- 
ure Retest the whole milk in the hand machine 
and compare the results with those obtained m the 
steam machine. 

3 (a) Take the B. of H. lactometer reading 
of a sample of skimmed milk. See how much water 
it will take to lower the lactometer reading one 
degree. Great care must be taken to mix the water 
with the milk as the former is poured in. This is 



40 A DAIRY LABORATORY GUIDE 

best done by pouring the milk from one vessel to 
another. 

(b) S^e if one-half gram of salt will bring the 
reading back to where it was originally. 



A DAIRY LABORATORY GUIDE 4I 

STUDENT'S NOTES AND REPORT 



i2 A DAIRY LABORATORY GUIDE 

STUDENT'S NOTES AND REPORT 



A DAIRY LABORATORY GUIDE 43 

EXPLANATION. ACIDITY OF MILK 

The acidity of milk is of two kinds — apparent 
and real acidity. The apparent acidity is due to 
the acid reaction of the acid phosphates and casein. 
The real acidity is due to the presence of lactic 
acid (C3H6O3), which is produced by the action of 
bacteria upon the sugar of the milk. The follow- 
ing reaction is supposed to be the one which takes 
place: 

Ci2H220ii + H20=-4C3H603 

The apparent acidity, according to Van Slyke, 
does not go above .08 per cent to .1 per cent, and is 
of minor importance so far as dairy work is con- 
cerned. In determining the acidity of milk it is as- 
sumed that all of the acidity is due to the presence 
of lactic acid. 

The real acidity will ordinarily go as high as I 
per cent, and in some cases, higher. Usually, how- 
ever, when from .8 per cent to i per cent acidity 
is reached the lactic acid organisms will cease 
working. If a part of the acid is neutralized the 
organisms will again commence the production of 
acid. 

Lactic acid is important in the manufacture of 
dairy products. For example, butter is churned 
from cream which is soured or " ripened " by lactic 
acid. The presence and amount of lactic acid is 
very important all through the process of cheese 
making. In many cases the nature of the product* 
depends on the amount of acid present during the 
successive steps of manufacture. 

For these reasons it is necessary to have soine 
means of finding the amount of acid in the milk. 
The process by which this is done is called titration. 



44 A DAIRY LABORATORY GUIDE 

It is a principle of chemistry that an alkali will 
neutralize an acid. In order, therefore, to find the 
acid in the milk we take a known quantity of the 
milk and measure into it an alkali whose strength 
we know. The instrument used to measure the 
amount of alkali used is called a burette, and the unit 
of measure is the cubic centimeter. It is commonly 
graduated as fine as tenths of a cubic cen- 
timeter. One can tell when all of the acid is neu- 
tralized by means of an indicator. The indicator 
used most in dairy work is phenolphthalein, which is 
colorless in acid and pink in alkali. If two or three 
drops of the indicator are put in milk the color will 
not change, because the milk is acid in reaction. 
The instant that just enough alkali is added to the 
milk to neutralize all of the acid the solution will 
turn pink. 

It is a chemical fact that equal volumes of acids 
and alkalies of the same chemical strength will ex- 
actly neutralize one another. In i cc. of a normal 
solution of lactic acid there are .09 grams of lactic 
acid. According to the above rule i cc. of any 
normal alkali solution would just neutralize .09 
grams of lactic acid. 

In actual practice a solution weaker than a normal 
solution is usually employed, because a normal solu- 
tion is so strong that any small variation in the 
amount used makes a big variation in results. A 
com.mon solution used is j/io normal (expressed 
n/io). One cc. of an n/io alkali solution would 
neutralize .009 grams of lactic acid. An example 
will illustrate how the per .cent of acid in milk is 
calculated. Suppose it took 6 cc. of n/io alkali 
solution to neutralize the acid in 20 grams of milk. 
What is the per cent of acid? One cc. of n/io alkali 
will neutralize .009 grams of lactic acid. Six cc. will 



A DAIRY LABORATORY GUIDE 45 

neutralize 6X.009=-054 grams of acid. .054-^20= 
.0027. .0027X100^.27% acid in the milk. Formu- 
lated, the above example is expressed as follows : 

:0^6^IOO=.27% 

If the milk for the acid test is measured in cubic 
centimeters it should be reduced to grams by mul- 
tiplying by the specific gravity of milk. The acid 
is obtained in terms of grams and we cannot divide 
grams by cc. and obtain per cent. 

Professor Farrington has devised some alkali 
tablets, each one of which will neutralize .03492 
grams of lactic acid. These tablets are dissolved 
in water and an alkali solution made. The strength 
of the solution per cc. will vary according to the 
number of tablets used and the number of cc. of 
water in which they are dissolved. The indicator 
IS added to the tablets when they are manufactured. 
Consequently, when using an alkali tablet solution 
no phenolphtholein is needed. A concrete example 
will show how these tablets are used. 

Suppose that it required 15 cc. of an alkali tablet 
solution to neutralize the acid in 20 grams of milk. 
The tablet solution was made by dissolving five 
tablets in too cc. of water. What is the per cent 
of acid in the milk? 

.03492=grams of lactic acid one tablet will neu- 
tralize. .03492X5=- 1 746 grams of lactic acid five 
tablets will neutralize. Since the five tablets are 
dissolved in too cc. of wnter .1746 is the amount of 
lactic acid too cc. of the solution will neutralize. 
Then . 1746-^100=. 00 1746, the strength of i cc. of 
the solution ; in other words, the number of grams 
of lactic acid i cc. of the solution will neutralize. 

.ooi746Xi5=-026i90 

.026I90-^2o=.ooI3095XIOO=.I3095% 



46 A DAIRY LABORATORY GUIDE 

If five of the alkali tablets are dissolved in 97 cc. 
of water each cubic centimeter of the solution will 
neutralize .01 per cent of acid when 18 grams of 
milk are used. This solution is often used by 
creamerymen, as the per cent of acid may then be 
read directly from the burette. Many devices for 
testing the acidity of ^ilk are on the market, all 
tending to do away with computation and giving 
the percentage of acid directly. One of these is 
Publow's acidimeter. In this apparatus an n/io 
alkali solution is used and 9 grams of milk are 
tested. Each cc. on the burette equals .1 per cent 
of acid and each i/io of a cc. equals .01 per cent 
acid. In testing for acid one should always try 
and obtain the same degree of color each time. 
This color" should be permanent for at least one 
minute. Great care should be taken not to run in 
an excess of alkali. It will be much easier to detect 
the color change if some ^vater is added to the 
sample after it is measured out before the alkali 
is added. 



A DAIRY LABORATORY GUIDE 47 

EXERCISE VIII 
BABCOCK TEST AND AClD TEST 

I (a) Test by the Babcock method, butter, cream 
and whole milk. Compute the weight of 
the fat column in the cream test. 
(b) Retest the whole milk, putting 9 grams in 
one bottle and 5 grams in the other. Re- 
duce each reading to a basis of 18 grams. 

2. (a) Test the skimmed milk for per cent of acid, 
using n/io alkali solution, and using 
17.6 cc. of milk. Do not add water to the 
sample. 

(b) Retest the skimmed milk, using 25 cc. of 

milk and compare with first test. 

(c) Measure out 18 grams of skimmed milk and 

add to this 17.6 cc. of water. Test for 
acid and compare with the first test. 

(d) Measure out 20 cc. of skimmed milk from 

same sample as used in above experi- 
ments and add to it 3 cc. of buttermilk 
or starter and test for acid. What is 
the object of using different amounts in 
(a) and (b)? What is the object of 
adding water to (c) ? 

3. Take the B. of H. lactometer reading of the 

whole milk and compute per cent of T.S. 
and S. N. F. 

4. Take a B. of H. lactometer reading of skimmed 

milk. Cool the milk as low as possible 
and compute what the reading would be 
at this temperature. Then compare your 
computation with the actual reading. 



48 A DAIRY LABORATORY GUIDE 

Perform the same experiment, heating the milk 
to 95° F. The object of this experiment is 
to show the incorrectness of a correction 
factor when used at a temperature of more 
than 10° F., either above or below 60° F. 



I 

A DAIRY LABORATORY GUIDE 49 

STUDENT'S NOTES AND REPORT 



50 A DAIRY LABORATORY GUIDE 

STUDENT'S NOTES AND REPORT 



A DAIRY LABORATORY GUIDE 51 

EXPLANATION. EFFECT OF SPEED OF 
MACHINE ON BABCOCK TEST 

The following exercise illustrates the influence of 
the speed of the machine on the amount of fat 
broug-ht to the surface. The speed of the machine 
is important, because the greater the speed the more 
force exerted. One should always run a Babcock 
tester up to the speed indicated in the directions for 
running the machine. Sometimes one will make as 
good a test when running a machine slow as when 
running faster. This, however, is not always the 
case, and in operating the tester one must be sure 
that the machine is run fast enough to bring all of 
the fat into the neck of the bottle. 



S2 A DAIRY LABORATORY GUIDE 

EXERCISE IX 
BABCOCK TEST AND LACTOMETER 

1. (a) Test by the Babcock method a sample of 

whole milk, skimmed milk and butter. 

(b) Retest the butter in the hand machine. 

(c) Retest the whole milk in tjie steam ma- 

chine, but do not let the speed of the 
machine exceed 250 revolutions per 
minute. 
In performing- the above experiment it is 
best to experiment with the machine 
before putting- in your samples. Other- 
wise, you will be liable to run the ma- 
chine too fast. 

2. (a) Take a lactometer reading of the whole 

milk and figure out the S. N. F. and 
T. S. 
(b) Take a lactometer reading of the skimmed 
milk and figure out the S. N. F. and T. S. 

3. (a) Test the skimmed milk for acid with n/io 

alkali solution and the alkali tablet solu- 
tion. The alkali tablet solution was 
made by dissolving eight tablets in 95 cc. 
of water. 
(b) Test for acid 18 grams of tap water. Add 
to 18 grams of tap water 3 cc. of starter 
or buttermilk, again test for acid. Use 
n/io alkali solution. 



A DAIRY LABORATORY GUIDE 53 

STUDENT'S NOTES AND REPORT 



54 A DAIRY LABORATORY GUIDE 

STUDENT'S NOTES AND REPORT 



A DAIRY LABORATORY GUIDE 55 



EXERCISE X 

BABCOCK TEST. LACTOMETER READING 
AND ACID TEST 

1 Make a Babcock test of cheese, whole milk and 

skimmed milk. Add acid to the skimmed 
milk about one-quarter of an inch above the 
usual mark, and run ten minutes, two mm- 
utes and one minute. 
Run the whole milk the usual time at the usual 
speed Be sure to cut the cheese fine before 
putting into the test bottle. 

2 (a) Retest the whole milk, running the machine 

one minute, one minute, one mmute. Be 
careful to run the machine at the same 
speed at which it was run the first time. 
Do you get any different results either m 
the amount or the appearance of fat? It 
so give the reasons. 
(b) Retest the whole milk, running the machine 
fifteen minutes, five minutes and three 
minutes. Do you get any more fat than 
when the machine is run the usual length 
of time' Be careful to run the machine 
at the same speed at which it was run 
the first time. 
Oil the machine well before each run. 
7 Take the B. of H. lactometer reading of skimmed 
^- milk and whole milk. Make corrections for 

temperature and figure out the S N. F. and 
T. S. for whole milk, using three formulae. 



56 A DAIRY LABORATORY GUIDE 

4. Test the whole milk for acid, using 18 grams. 
Use both n/io and alkali tablet solution. 
Test the skimmed milk for acid, with the iVio 
solution. Use only 5 cc. of the milk. Do this 
twice, so that one result will be a check on 
the other. Again test the skimmed milk, 
using a 50-cc. sample. Do this twice. See 
if you get the more uniform results with the 
large sample. 



STUDENT'S NOTES AND REPORT 



A DAIRY LABORATORY GUIDE S7 

STUDENT'S NOTES AND REPORT 



58 A DAIRY LABORATORY GUIDE 

EXPLANATION OF EXERCISE XI 

In testing butter by the Babcock method, the 
practice is sometimes followed of melting the 
butter and then putting it into the test bottle 
by means of the pipette. It is posssible to do 
this sometimes and get accurate results, but 
the tendency for fat and water to separate 
makes it difficult to get accurate tests. 

Division b of experiment 2 illustrates how 
readily the fat and water separate. In draw- 
ing off the fat for this experiment, keep the 
point of the pipette at the surface of the fat. 

Carbon dioxide acts toward an alkali like an 
acid. We are told that some of the acidity 
of the milk is due to the presence of CO2. 
In experiment 4, pouring the milk back and 
forth from one vessel to another tends to mix 
the CO2 of the air with the milk. Heat will 
expel the CO2, and so after boiling the milk 
the acid test would be lower than it would 
be before boiling. This experiment also 
shows that milk will take up gases. 

In the same way that acids and alkalies form 
reactions so do solutions of certain salts form 
reactions. When salts do react they follow 
the same rule as acids and alkalies, namely, 
that equal volumes of salts of the same chem- 
ical strength will just neutralize one another. 
This fact is made use of in determining, 
quantitatively, the amount of salt (sodium 
chloride) in butter. The salt used to neutral- 
ize the sodium chloride is silver nitrate (Ag 
N03) and the indicator used to tell when 
enough silver nitrate has been added is a solu- 



A DAIRY LABORATORY GUIDE 59 

tion of potassium chromate (K2Cr O4). This 
indicator added to sodium chloride solution 
produces a lemon yellow color. When enough 
silver nitrate has been added to just neutral- 
ize all of the sodium chloride the solution 
turns a light brown color. No more silver 
nitrate should be added when a permanent 
light brown color is obtained. 

The chemical reaction which takes place is as 
follows : 

Nacl+Ag No3=Na Nog+Agcl 

One cc. of n/jo silver nitrate solution will neu- 
tralize .00585 grams of sodium chloride. Since 
the butter is in solid form, it is necessary to 
dissolve the sodium chloride and this is done 
by washing the butter in a definite amount 
of warm water, and titrating the water. 

Suppose 10 grams of butter are washed in 200 
cc. of warm water and it takes 6 cc. of silver 
nitrate solution to neutralize the salt in 50 cc. 
of the wash water. It would then require 24 
cc. of silver nitrate solution to neutralize the 
salt in 200 cc. of wash water. Since i cc. of 
silver nitrate will neutralize .00585 grams of 
salt (sodium chloride) 24 cc, will neutralize 
.1404 grams of salt (24x.oo585=.i404). 

This salt was obtained from 10 grams of butter 
so .1404 grams of salt divided by 10 grams of 
butter, and the quotient multiplied by 100 
will give 1.404 the per cent of salt in the but- 
ter. 



6o A DAIRY LABORATORY GUIDE 

EXERCISE XI 
BABCOCK TEST AND ACID TEST 

1. ]\Iake up an alkali tablet solution as directed. 

Shake frequently, and set aside for use later 
in the exercise. 

2. (a) Test by the Babcock method a sample of 

whole milk and a sample of butter. 
(b) Place a piece o*f butter in your acid measure 
and allow it to stand in a cup of hot 
water for about fifteen minutes. Then 
with a pipette draw the fat from the sur- 
face of the liquid. Weigh out the proper 
amount and test by the Babcock method. 
What conclusions do you draw from this 
experiment ? 

3. Test for acid a sample of starter, using the 

alkali tablet solution furnished and n'lo 
alkali solution. Use 3 cc. of starter. 

4. Pour back and forth from one vessel to another 

about 100 cc. of skimmed milk. Do this for 
about three minutes. Test 25 cc. of it for 
acid, using the alkali tablet solution which 
you made up at the beginning of the exer- 
cise. Then boil about 35 cc. of the milk for 
about one minute ; cool ; keep covered while 
cooling, and retest 25 cc. for acid. Compare 
with first test and see if you get lower re- 
sults. 

Explain fully why lower results may be ex- 
pected with boiled milk. 

The alkali tablet solution was made by dissolv- 
ing 10 alkali tablets in 115 cc. of water. 



A DAIRY LABORATORY GUIDE 6t 

STUDENT'S NOTES AND REPORT 



6^ A DAIRY LABORATORY GUIDE 

STUDENT'S NOTES AND REPORT 



A DAIRY LABORATORY GUIDE 63 



EXERCISE XII 

BABCOCK TEST AND BUTTER MOISTURE 
TEST 

1. Test a sample of cheese, whole milk and 

skimmed milk for butter fat. In testing the 
skimmed milk, run extra time and use extra 
acid as previously directed. 

2. Test cheese for acid, using n/io alkali solution. 

In order to test cheese for acid, weigh out 3 
grams. Place in a white cup and add 17.6 cc. 
of warm water. Then with a stirring rod 
grind the cheese up as fine as possible. This 
will take at least five minutes. Then test 
the solution as usual, and calculate the per 
cent of acid. 

3. Test a sample of butter for moisture by the 

Cornell method. 

4. Test for salt a sample of butter, using an n/io 

silver nitrate solution. Use 10 grams of but- 
ter and 250 cc. of water. Titrate at least three 
50 cc. portions of water and check results 
carefully. 



Note. — To what is the high acid content of cheese 
due? 



64 A DAIRY LABORATORY GUIDE 

STUDENT'S NOTES AND REPORT 



A DAIRY LABORATORY GUIDE 65 

STUDENT'S NOTES AND REPORT 



66 A DAIRY LABORATORY GUIDE 



EXERCISE XIII 

BABCOCK TEST, LACTOMETER AND ACID 

TEST 

1. Test by the Babcock method a sample of whole 

milk, cottage cheese and buttermilk. Fill 
your lightning top sample jar about one-third 
full of whole milk, add a preservative tablet 
and shake at intervals until tablet is dis- 
solved. Set the sample away in your desk 
and test at the next exercise. 
Use 9 grams of cottage cheese, and add 9 grams 
of water. Test in whole milk bottle. Shake 
well after adding acid. 

2. To about 54 grams of skimmed milk add 2 cc. 

of light machine oil, shake thoroughly. Using 
the whole milk test bottle, test the sample 
in duplicate by the Babcock method. Com- 
pare the appearance of the fat column with 
that obtained with ordinary butter. 

3. Test with the alkali tablet solution the acid in 

the whole milk and buttermilk. 

4. Take a lactometer reading of the whole milk. 

Add some water (about 25 cc.) to the 
sample. Again take a lactometer reading 
and make a Babcock test. Figure out T. S. 
and S. N. F. and the per cent of the water 
added. 

5. Test for salt a sample of butter using 10 grams 

of butter and 300 cc. of water. Titrate sev- 
eral 17.5 cc. portions of the water and check 
results carefullv. 



A DAIRY LABORATORY GUIDE 6/ 

STUDENTS NOTES AND REPORT 



68 A DAIRY LABORATORY GUIDE 

STUDENT'S NOTES AND REPORT 



A DAIRV LABORATORY GUIDE 69 

EXPLANATION. COMMERCIAL RENNET 
AND ITS USE 

Commercial rennet is a liquid prepared by soak- 
ing: in brine the fourth stomach of the calf. It has 
under certain conditions the power of precipitating 
the casein from milk. It is so desirable for this 
purpose that rennet is used almost exclusively in 
the manufacture of cheese. One peculiar character- 
istic of rennet is the fact that it is not destroyed 
by its use in precipitating casein. If it could be 
extracted the same rennet could be used over and 
over again for precipitating the casein in different 
lots of milk. 

Temperature has a decided effect upon the action 
of rennet. The colder milk is, the less rapid the 
rennet action. This is very noticeable at tempera- 
tures below 80° F. The rennet acts most rapidly 
at temperatures from ioo° F. to 120° F. At 130° 
F. the action of the rennet is less active and its 
action is entirely destroyed somewhere between 
140° F. and 150° F. The high temperature destroys 
the rennin, which is the active principle of the 
rennet. The action of rennet increases as the acid 
in the milk increases. The action of rennet seems 
to depend to a great degree upon the solubility of 
the lime salts of the milk. If an insoluble lime 
salt is added to the milk, the action of the rennet 
is retarded, and if a soluble lime salt is added to 
milk the action of rennet is hastened. If milk is 
heated to a high temperature the lime salts are 
supposed to be rendered insoluble and the rennet 
has no effect on the casein. Freezing does not seem 
to injure rennet. When it is again melted and 
given the proper temperature it will act as though 
it had never been frozen. 



70 A DAIRY LABORATORY GUIDE 



EXERCISE XIV 

BABCOCK TEST, MICROSCOPIC APPEAR- 
ANCE OF MILK, USE OF RENNET 

1. Test the composite sample preserved at the last 

exercise. 

2. Examine under the high-power microscope 

cream, whole milk and skimmed milk. Make 
a drawing of each field. Describe fully the 
difiference in the appearance of the fat 
globules in each of the three fields. 

3. Heat 18 grams of skimmed milk to about 100° 

F. and add four drops of rennet ; shake thor- 
oughly and let stand. Note the length of 
time it takes the milk to curdle. 

4. To one-half a teacup of water add six drops of 

sulphuric acid. Add three drops of this solu- 
tion to 18 grams of milk. Heat to about 
100° F. and add four drops of rennet and 
note the time it takes for milk to coagulate. 
Compare length of time with that required 
in No. 3. 

5. To about 20 grams of skimmed milk add six 

drops of sulphuric acid and shake thoroughly. 
Note time it takes the milk to coagulate and 
compare the coagulum with that obtained 
when rennet is used. 

6. Measure out two 25 cc. samples of skimmed 

milk. Warm to 80° F. To one sample add 
five drops of rennet ; to the other add five 
drops of sulphuric acid. Note and compare 
the length of time it takes each to coagulate. 
What two things hasten the action of rennet 
in milk? 



A DAIRY LABORATORY GUIDE 7! 

STUDENT'S NOTES AND REPORT 



72 A DAIRY LABORATORY GUIDE 

STUDENT'S NOTES AND REPORT 



A DAIRY LABORATORY GUIDE 73 

EXERCISE XV 
BABCOCK TEST AND USE OF RENNET 

1. Test by the Babcock method a sample of butter- 

milk and a sample of skimmed milk cheese 
and whole milk cheese. Compare the results 
of the cheese tests. 

2. Boil a sample of milk for about two minutes 

and then cool. Add some rennet and see if 
the milk will coagulate. State the amount of 
milk and rennet used. 

3. Boil 25 cc. of milk for about two minutes and 

then cool. Add one-half cc. of sulphuric acid 
and see if the milk will coagulate. 

4. Add to 25 cc. of milk six drops of rennet. Have 

the temperature of the milk at ioo° F. Note 
the time it takes the milk to coagulate. Test 
25 cc. of the same lot of milk for acid. Com- 
pute the amount of n/io alkali necessary to 
neutralize the acid in 50 grams of the milk. 
Add this alkali to the 50 grams of milk. 
Divide the milk into two portions of 25 cc. 
each and bring the temperature of each to 
100° F. and add to each six drops of rennet. 
Note the tim^e it takes the samples to co- 
agulate. Compare with the length of time 
required to coagulate the milk before the 
alkali was added. 



; 



^74 A DAIRY LABORATORY GUIDE 

STUDENT'S NOTES AND REPORT 



A DAIRY LABORATORY GUIDE 75 

STUDENT'S NOTES AND REPORT 



76 A DAIRY LABORATORY GUIDE 



EXERCISE XVI 

BABCOCK TEST AND LACTOMETER 
READING 

Take a lactometer reading and make a Babcock 
test of a sample of whole milk. Compute the 
T. S. and the S. N. F. Allow the sample to 
stand in the lactometer cylinder while you 
do No. 2. Then remove all of the cream pos- 
sible and add 25 cc. of water. Ag"ain make 
a Babcock test, and take a lactometer read- 
ing. Compute the per cent of water added, 
the rate per cent at which water was added, 
the per cent of fat removed by skimming, 
the per cent of fat removed by watering and 
the rate per cent at which the fat was re- 
moved. 

Test in the steam machine a sample of whole 
milk, and a sample of butter. Retest a 
sample from the same lot of milk in 
the hand machine and fill the machine 
with water at 60° F. Note the result 
of the low temperature upon the fat column. 
Run the same bottles which were tested in 
the hand machine in the steam machine for 
a period of three minutes and then read the 
fat column. N^ote if there is any increase 
in the fat column. 



A DAIRY LABORATORY GUIDE 77 

STUDENT'S NOTES AND REPORT 



^S A DAIRY LABORATORY GUIDE 

STUDENT'S NOTES AND REPORT 



A DAIRY T.ADORATORV GUIDE 79 



EXERCISE XVII 

USE OF RENNET. PRECIPITATION OF 

ALBUMEN 

1. Take i8 grams of milk in a white cup and cool to 

50° F. Add four drops of rennet and note 
time it takes the milk to coagulate. Com- 
pare this with the same amount of milk 
warmed to 85° F., to which four drops of 
rennet have been added. 

2. Boil some whey and note the albumen which is 

thrown down in a white flocculent pre- 
cipitate. Fill your lightning top sample jar 
about one-half full of skimmed milk at about 
100° F. Add I cc. of rennet. Set aside to 
coagulate. Then strain ofif the whey and 
precipitate the albumen in the whey by boil- 
ing. 

In both cases the boiling should be done in a 
test tube. It may at first be difficult to see 
albumen, as it is in very fine particles. The 
albumen may be distinguished more readily 
by holding the test tube between the eye and 
the window. 

Turn in desk, key and locker. See that all glass- 
ware is clean before turning in the desk. 



80 A DAIRY LABORATORY GUIDE 

STUDENT'S NOTES AND REPORT 



A DAIRY LABORATORY GUIDE 8 1 

STUDENT'S NOTES AND REPORT 



INDEX 



PAGE 

Aci<l: 

Lactic ^"^ 

Measure '^ 

In Milk 4;^ 

Sulphuric ^ 

Acidity : 

Apparent and real *^ 

As effected by CO. ^■• 

Alkali Tablet Solution 45 

Babcock Test ^^ 

Boiled Milk Test 1^ 

Burette ^^ 

Butter Fat I 

Melting point ^ 

Moisture in }^ 

Preparation for fat test l^ 

Preparation for moisture test 23 

Casein 

Amount in milk ^ 

Characteristics of ;^; 

Commercial uses of ^* 

Collodial state ^ 

Cornell Moisture Test 23 

Cream 

Viscosity of ^ 

Weighing for testing ' 

Fat I 

Composition of 

Formaldehyde Test 1^ 

Galactase ^^ 

Indicator '^^ 

Lactometer ;^ 

Board of Health ^ ' 

Quevenne ^^ 

Uses of ~" 

Machines ^\ 

Hand • ;^ 

Effect of speed on test -^^ 

Melting Point of Butter Fat -^ 

83 



84 DAIRY LABORATORY GUIDE 



PAGE 

Milk 1 

Adulteration 31 

Albumen in 4 

Ash in 4 

Composition of 1 

Casein in 3 

Fat in 2 

Sugar in 4 

Water in 1 

Phenolphthalein 44 

Pipette 5 

Reading Fat Colun.ii 6 

Rennet 09 

Effect of acid on action (il) 

Effect of temperature on action 69 

Salt, test for 59 

Solids Not Fat 29 

Formulae for finding 29 

Specific Gravity 27 

Of milk 27 

Testing : 

Butter 8 

Cheese 8 

Cream "^ 

Skimmed w.'u'k 7 

Whey 9 

Whole milk 5 

Temperature : 

Effect on lactometer reading 28 

Effect on fat column 6 

Effect on rennet action 69 



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